Proteolysis of Livanjs']jski cheese during ripening

Livanjski cheese belongs to the group of hard cheeses which is traditionally produced in Livno (Bosnia and Herzegovina). Proteolytic changes during the ripening of Livanjski cheese have not been investigated extensively. The aim of this paper was to determine its proteolytic changes during the different stages of ripening. Five Livanjski cheeses (from raw cow's or a mixture of sheep's and cow's milk) were observed during the ripening to evaluate its typical proteolytic profile. An electophoretic profile of Livanjski cheese was determined by Urea-polyacrylamide gel electrophoresis (urea-PAGE) and a densitometric evaluation of the urea-PAGE gels was performed using a densitometer. The water-soluble nitrogen fraction in the total nitrogen (WSN % TN) and the 12%-TCA-soluble nitrogen fraction in the total nitrogen (TCA-SN % TN) of the cheese were determined using the Kjeldahl method. Degradation of alpha(s1)-casein by chymosin caused a significant decrease (P < 0.05) of relative content of this protein in Livanjski cheese at the sixth week point of ripening. Due to the activity of chymosin on as1-casein, alpha(s1)-I-casein and alpha(s1)-II-casein developed, which caused a significant increase (P < 0.05) of Index alpha. The relative ratio of beta-casein significantly decreased (P < 0.05) during ripening leading to a significant accumulation (P < 0.05) of degraded product (sum gamma(1)-casein,gamma(2)-casein and gamma(3)-casein). These proteolytic changes caused a significant increase (P < 0.05) of Index betta. Accumulation of medium, small peptides and amino acids caused a significant (P < 0.05) increase of the relative content of WSN % TN and TCA-SN % TN. In general, proteolysis of Livanjski cheese during ripening was moderate probably due to the low moisture content and low water activity, although it was produced from raw milk. Taking into account that the ratio beta-casein : alpha(s1)-casein at the end of ripening was 1.46, it could be concluded that degradation of alpha(s1)-casein could be the indicator of the maturity of Livanjski cheese. Due to that Livanjski cheese could be classified as "alpha-type of ripening" cheese.